Neanderthals in gene pool, study suggests

Scientists have found new genetic evidence they say may answer the longstanding question of whether modern humans and Neanderthals interbred when they co-existed thousands of years ago. The answer: probably yes, though not often.

In research published by the Proceedings of the National Academy of Sciences, the scientists reported that matings between Neanderthals and modern humans presumably accounted for the presence of a variant of the gene that regulates brain size.

Bruce T. Lahn of the University of Chicago, the report's senior author, said the findings demonstrated that such interbreeding with relative species, those on the brink of extinction, contributed to the evolutionary success of modern humans.

Other researchers in evolutionary biology said the new study offered strong support for the long-disputed idea that archaic species such as Neanderthals contributed to the modern human gene pool.

Genetic and fossil studies show that anatomically modern humans emerged 200,000 years ago in Africa and migrated into Europe 40,000 years ago. In about 10,000 years, Europe's longtime inhabitants, Neanderthals, became extinct. The mainstream interpretation is that modern humans somehow replaced them without interbreeding.

In previous research, Lahn and associates discovered that a gene for brain size called microcephalin underwent a significant change 37,000 years ago. Its modified variant, or allele, appeared to confer a fitness advantage on those who possessed it. It is now present in about 70 percent of the world's population.

The new research focused on the two classes of alleles of the brain gene. One appeared to have emerged 1.1 million years ago in an archaic Homo lineage that led to Neanderthals and was separate from the immediate predecessors of modern humans. The 37,000-year date for the other variant immediately suggested a connection with Neanderthals.

Lahn said it did not necessarily show that interbreeding was widespread. It could have been a rare, perhaps even single, event.